1. Technical Field
The present invention relates to a navigation apparatus and more particularly, to a navigation apparatus operable to perform route guidance by using a camera image obtained by shooting a scene ahead of a vehicle.
2. Background Art
Conventionally, in widespread use is a navigation apparatus which performs route guidance by searching a route from a current self-position of a vehicle to a destination which has been set and by using map data accumulated with respect to branching points present on the route. In recent years, owing to an increase in a capacity of a storage medium such as an HDD and a DVD, a navigation apparatus is capable of storing further detailed map data. In pursuit of easy viewability and reality of a guidance display, a variety of map representations, such as a three-dimensional bird's-eye view representation and a driver's view presentation using realistic three-dimensional CG, have been adopted.
In addition, there has been proposed a driving guide image displaying method used in an on-vehicle navigation apparatus. In the method, an image of a scene ahead of a vehicle is obtained by using shooting means such as a video camera and when the vehicle approaches an intersection to which the vehicle is to be guided, a guide arrow is displayed in the image of the scene ahead of the vehicle in a superimposed manner as route information indicating a route in the intersection, along which the vehicle is to travel, thereby performing further accurate and easily viewable route guidance (refer to Patent Document 1).
[Patent Document 1] Japanese Patent Application Laid-Open Publication No. 7-63572
However, the conventional method is not capable of dynamically changing a frequency of updating a shape of the guide arrow. In reality, when a distance to an intersection to which the vehicle is to be guided is large, no deviation of the guide arrow to be displayed in the camera image occurs and therefore, the frequency of updating the guide arrow can be set to be low (for example, a frequency of one time per second); and when a distance to an intersection to which the vehicle is to be guided is small, a deviation of the guide arrow to be displayed in the camera image increases and therefore, the frequency of updating the guide arrow can be set to be high (for example, a frequency of three times per second), whereby an appropriate frequency of updating the guide arrow varies depending on circumstances.
Accordingly, in the conventional method in which the shape of the guide arrow is updated at an invariably constant frequency, in a case where an updating frequency of drawing the arrow, which has been previously set, is low, a deviation of the guide arrow to be displayed in the image in the vicinity of an intersection to which the vehicle is to be guided increases, thereby resulting in poor viewability of a guide display. In addition, in a case where a previously set frequency of updating the guide arrow is high, the guide arrow is updated at a high frequency even in the situation where a high updating frequency is not intrinsically required, such as the situation where a distance to an intersection to which the vehicle is to be guided is large, thereby leading to an increase in a processing load exerted on the navigation apparatus.
In consideration of the above-described problem, the present invention was made. In other words, an object of the present invention is to provide a navigation apparatus operable to, in route guidance using a photographed image, dynamically set a frequency of updating the guide arrow in accordance with circumstances.